DE102020104689A1 - Device and method for material removal from fiber composite materials, in particular for shafts - Google Patents

Abstract

The present invention relates to the field of material removal from fiber composite materials and, in particular, material removal for the creation of shafts, as is provided, for example, when a fiber composite is repaired with fiber and resin. A method and a corresponding device are proposed, the method providing a pressure gradient in a transport gas, providing a blasting material, accelerating the blasting material through the pressure gradient on a surface of the fiber composite workpiece, abrasive removal of material including fibers and resin from the Provides fiber composite work piece in a working space determined by a removal unit and the fiber composite work piece and removal of removed material and blasting material from the work space through the pressure gradient, whereby the blasting material is guided through a nozzle onto the surface of the fiber composite work piece, the blasting material has an average grain size in the range of 200 µm up to 500 µm and the distance between the jet pipe and the fiber composite workpiece in the working area is in the range from 3 to 12 mm.

Description

The present invention relates to the field of material removal from fiber composite materials and, in particular, material removal for creating a shaft, as is provided, for example, when a fiber composite is repaired with fiber and resin.

Fiber composite structures and laminates are increasingly used in the aviation, wind and automotive industries. Frequently, damage to these structures occurs through, for example, high-speed impacts. One of the major challenges facing the industries is the traditionally expensive and time-consuming repair of the fiber composite. Nowadays, in order to repair fiber composite components, they have to be laboriously processed in that the damaged layers are first removed individually. This is done by creating formwork geometries (shafts). The removal processes for repairs and processing on fiber composite components, which are mostly carried out manually nowadays, are extremely polluted with emissions and require a lot of time from the preparation to the post-processing of a clean processing point. Here, environmental and health aspects also play a major role. The speed and quality of the removal process is also heavily dependent on the experience of the worker.

Automation solutions currently under development have many limitations and disadvantages, especially with regard to the quality and accuracy of the machining. In the industrial use of an automated removal system, special attention is paid to emission-free processing and the most universal usability possible (location-independent, different FRP components, different industries) in order to cover a wide range of applications (see e.g. "Composite Repair", publication UTC 102, April 1999, from Hexel Composites, Duxford). From the point of view of immission control, when removing the individual layers, suction or subsequent cleaning must ensure that all dust and residual dirt are removed in order to avoid contamination.

High removal rates and extensive, in-depth removal with consistent quality are new challenges in the area of automated processing of repair points on fiber composite components (see e.g. N. Bhatnagar, N. Ramakrishnan, NK Naik, R. Komanduri "On the machining of fiber reinforced plastic (FRP) composite laminates." International Journal of Machine Tools & Manufacture 1995 ; 35 (5): 701-716). Standardization and automated, ie quality-assured, regulation is necessary, which brings a considerable advantage in terms of time. Automated systems are also mostly expensive, difficult to transport and require a lot of space.

Currently, there are challenges in particular with regard to a large variety of materials, excessive pre-, post-cleaning and post-processing times, the lack of standardized procedures for the automation of the removal process, the lack of process-accompanying quality control today and corresponding sensors, the freedom from immissions or at least restrictions in automated processes Surfaces, the weight and space requirements of automated processes, the precision of the automated removal, the laborious manual work and subsequent cleaning work that is still necessary, the associated safety and health risks, the lack of automated in-field technology and the lack of an approved automated removal process for fiber composite materials.

The currently approved repair process for fiber composite materials includes the removal of the damaged fiber composite layers before the patch repair layers are glued to the removed area. A large area of fiber composite must be removed around the damaged area. The individual layers of composite structures must be processed and removed until all the damaged layers underneath have been removed. The layers are usually removed using a stepped or conical shape of the scarf. As explained in the article "Repair of fiber composite components" (F. Ellert, Lightweight-Design Journal, 03/2015), the process flow of a repair of fiber composite components usually includes the process steps of an assessment of the processing damage area, categorization, pre-cleaning, removal of Individual layers, subsequent cleaning, production of a repair patch and gluing or lamination of the repair patch including curing. Finally, depending on the area of application, an NDT test is carried out as a check (see, for example, Wachinger G., Thum C., Scheid P .: "Repairability and repair concepts for structures made of fiber-reinforced plastics", in Henning F., "Handbuch Leichtbau" Munich: Hanser Publisher, 2011)

With a few exceptions, the process of removing fiber composite materials is currently carried out by manual grinding, which a worker has to carry out using a hand-held electric or compressed air grinder. As a result, the result depends significantly on the level of knowledge and the skill of the specialist staff. Different Materials and imperfections of different strengths require a treatment strength that is adapted to each application. The control is only carried out by means of a visual inspection. When removing manually, the worker must wear protective clothing to protect himself from the fiber composite dust. There is a major health risk here. In addition, from an ergonomic point of view, manual processing is a heavy physical strain for the worker, since the precise removal with the heavy grinding devices and the mechanical forces that occur during contact processing require a great deal of endurance (see e.g. F. Cenac, F. Collombet, R. Zitoune and M. Deleris, "Abrasive-water-jet blind-machining of polymer matrix composite materials", Universite de Toulouse). Compressed air blasting uses a high speed stream of solid abrasive particles to remove the material. This is mainly carried out in blasting cabins in order to be able to extract the dust. The worker must wear a protective suit.

For aviation there is currently no globally approved automated process for removing damage to fiber composite components, e.g. for in-field repairs on CFRP fuselages on the B787 and A350. Automated, mechanical material removal is currently being tested with milling machines, almost exclusively in the prototype stage.

Disadvantages are complex post-cleaning processes at the repair site, the time taken, costs, size and weight of the machines and the positioning of the tools. To avoid immission, large milling booths are built and complex suction devices are integrated for cleaning the booths and components (see Dittmar, Hagen; laser-based repair preparation of composite structures, LZH; 2017). Milling uses carbide or diamond tools to machine and remove the fiber composite material (see 1 ). The effective speed is directed tangentially to the workpiece surface. The resulting forces cause strong intralaminar and interlaminar shear stresses in the fiber composite, as a result of which there is a risk of delamination and fiber pull-out in the composite and, on the surface, loose fiber ends loosened from the composite arise. In addition, the contact of such tools also creates thermal stresses in the component. Developments with regard to laser ablation, which must be tailored to the materials in each case, are processes that take a lot of time, have a high level of heat dissipation into the processing point and the environment, and require a large amount of equipment. The accuracy and precision of the ablation is very limited, especially in the edge and transition area of the layers (see also Dittmar, Hagen; laser-based repair preparation of composite structures, LZH; 2017). Water jet cutting (AWJ) is a wet removal process with high system costs and large space requirements. Above all, the process harbors the risk of uncontrolled contamination during the repair of the finished structure (see also F. Cenac, F. Collombet, R. Zitoune and M. Deleris, "Abrasive-water-jet blind-machining of polymer matrix composite materials" , Universite de Toulouse).

Further information on the repair of fiber composite materials can also be found in "Adaptive Machining for Efficient Manufacture and Repair of CFRP Components" by Claus Bremer (BCT GmbH, 6/2012) and "Care and repair of advanced composites" by K.B. Armstrong, W.F. Cole, L.G. Bevan (SAE International, London 2005).

Approaches to the detection of damaged areas are already known and possible with methods of radiography, ultrasound or thermography (see e.g. training material SKZ Kunststoffzentrum; "Detecting damage to CFRP components", www.skz.de). A measurement of untreated fiber composite surfaces with 1D / 2D line scanners for distance control and inline path corrections for automatic robot movements was considered at Fraunhofer IFAM in Stade in past and ongoing projects.

A fully automatic control of removed layers and subsequent path control by means of sensors during the removal process has not been available in the industry up to now and represents a particular challenge with the approaches followed up to now visual control of the worker checked (see e.g. EP 2 442 941 B1 ).

Some of the technologies described above for automated or partially automated stocks have been known for a long time and are also available on the market. Due to their principle-related technological limits, disadvantages and risks, they have so far not been able to prevail over manual stocks.

The vacuum suction blasting process (as an example of a blasting process) has so far only been used to remove impurities from the surface or to remove cover layers from fiber composite materials (i.e. without removing the fiber itself), e.g. for thin-layer roughening or activation before bonding.

A vacuum suction jet unit comprises three main components: a jet nozzle unit, an industrial vacuum cleaner and a material feeder. The blasting medium is conveyed to the workpiece surface to be treated by negative pressure via a pipe and hose system. The necessary vacuum is generated by the industrial vacuum cleaner and the blasting material is accelerated from a storage container. The blasting media transport consists of a supply unit and a suction unit, which are sealed with the surface in a vacuum-tight manner. The removal mechanism on the surface takes place at the blasting head. After the blasting material has hit the workpiece surface there and removes it there, the remaining particles and removed workpiece particles are removed via the suction system. This results in a clean workpiece surface after blasting. Advantages of vacuum suction blasting compared to conventional sandblasting methods include lower pressure and therefore less stress on the component as well as emission-free treatment. Commercial vacuum suction blasting systems are offered, for example, for deburring metal surfaces (see Ruhland, Sigurd: Vacuum suction blasting in the production line, GP Innovation GmbH, JOT 7, 2014). Manual processing by means of a hand-held moving jet lance is used, for example, to remove layers of paint and to roughen up before gluing.

Already known approaches in connection with vacuum suction beams are, for example, in DE 10 2010 020 691 A1 , DE 19 747 838 C2 , DE 10 2010 060 664 A1 , EP 1 136 174 A1 , US 2004/053561 A1 or EP 2 442 941 B1 described.

The known approaches to vacuum suction blasting, however, allow - in so far as they - in addition to the resin in the composite workpiece - also remove the fibers at all, only such a low removal rate that they are not suitable as alternatives to manual shafting.

One aim of the present invention is to provide a method and a corresponding device for removing material from a fiber composite workpiece with fibers and resin, with which at least some disadvantages of the methods and devices currently used for such material removal, in particular for repair or repair preparation, are avoided or at least be reduced.

It is particularly desirable here to present a solution that can serve as the basis for extensive or even complete automation in the repair of a fiber composite workpiece.

According to a first aspect, a method for removing material from a fiber composite workpiece with fibers and resin is proposed, as defined in claim 1, namely with the steps of providing a pressure gradient in a transport gas, providing a blasting material, accelerating the blasting material through the Pressure gradient on a surface of the fiber composite workpiece, the abrasive removal of material including fibers and resin from the fiber composite workpiece in a working space determined by a removal unit and the fiber composite workpiece and the removal of removed material and blasting material from the working space through the pressure gradient, the blasting material through a nozzle is directed onto the surface of the fiber composite workpiece and the blasting material has an average grain size in the range from 200 µm to 500 µm and the distance between the beam pipe and the fiber composite workpiece in the work area is within one range from 3 to 12 mm.

According to a second aspect of the invention, a device for automated material removal from a fiber composite workpiece with fibers and resin is proposed as defined in claim 16, namely with a pressure unit that is designed to provide a pressure gradient in a transport gas, a material supply that is used to provide of a blasting material is designed, and a removal unit with a jet pipe, wherein the device is configured to accelerate and guide the blasting material provided by the material supply to a surface of the fiber composite workpiece through a pressure gradient provided by the pressure unit, so that an abrasive removal of Material including fibers and resin from the fiber composite workpiece is effected in a working space determined by a removal unit and the fiber composite workpiece, the device also for removing removed material and blasting material from the work eitsraum is designed by the pressure gradient, wherein the blasting material has an average grain size in the range of 200 microns to 500 microns and a distance of the jet pipe to the fiber composite workpiece in the workspace is in a range of 3 to 12 mm when the device is in operation.

Part of the background to the present invention resides in the following considerations.

It has been found that a known method such as vacuum suction blasting, which is only used for ablation close to the surface (less than 100 μm depth), can be used for material ablation relevant for shafts if the blasting material and the distance between the blasting tube and the surface are suitable .

However, vacuum suction blasting can only be used economically through the combination of the larger grain compared to the known approach and a smaller distance to the surface to be processed to remove material from the fiber composite work piece that is significant but nevertheless sufficiently precise.

The use of only one blasting material with a larger mean grain size while otherwise maintaining the parameters of the known approach to vacuum suction blasting (which was only intended for surface treatment) leads to a longer processing time, and the removal becomes more uneven.

In the present case, the mean grain size is determined by sieving (10 µm to button size). The grain size corresponding to a sieve passage of 50% is the "mean grain size" (MK). The percentage by weight of grains between the grain sizes 4/3 MK and 2/3 MK is called the "degree of uniformity" (GG).

A smaller distance between the jet pipe and the surface has little effect on the conventionally used blasting materials, and it has also been observed that the machining accuracy sometimes decreases, so that the removal becomes more uneven.

It has now been found, however, that the combination of the choice of the grain size of the blasting material together with the appropriate setting of the distance between the blasting tube surprisingly leads to a strong and correspondingly rapid material removal, in which the desired accuracy is also achieved.

Even if a realization of the invention in the form of a vacuum suction jet is preferred, it should be noted that within the scope of the invention a vacuum in the sense of a negative pressure compared to the normal atmosphere is not necessary as such, since basically every sufficiently dimensioned pressure gradient for transport and removal can be used by blasting material and removed material.

Since the release of dust and the like can be prevented or at least severely restricted with the present invention, a close control of the results of the material removal is also possible, which has an advantageous effect on the possibilities for automation.

The approach according to the invention is robust in relation to hybrid workpieces, i.e. workpieces made up of different types of material. Due to the principle, the forces locally applied to the workpiece surface are very small, especially with vacuum suction blasting, which is particularly advantageous when precision machining thin-walled lightweight structures. In contrast to the abrasion by the blasting material, the cutting edges of a cutting tool load the workpiece edge zone primarily tangentially in a linear zone. As a result, the tension introduced is less concentrated. In addition to the desired removal, inter- and intralaminar microcracks and fiber ends loosened from the surface of the composite result, which impair the adhesion of the workpiece surface and require a subsequent polishing operation.

With the known laser beam ablation, the extremely different thermophysical and optical properties of the components of fiber-reinforced plastics and possibly the properties of metallic cover layers are difficult to master. Depending on the material or combination of materials, the wavelength must be matched to their different absorption behavior. The very low decomposition temperature of the resin matrix and the extremely high sublimation temperature of carbon fibers imply the risk that the resin matrix in the vicinity of the processing point will be thermally damaged, resulting in inter- and intralaminar cracks and delamination. When fiber-reinforced plastics are ablated by laser, gaseous fission products that are harmful to health are created which, in view of the variability of the damaged areas to be processed, are difficult to detect near the point of action and therefore require a great deal of effort. These problems do not arise within the scope of the invention.

In contrast to methods with an active movement tangential to the component surface (e.g. milling, grinding), the approach according to the invention is characterized by an exclusive or predominantly normal active movement to the component surface. This enables the fibers to be separated without or largely without shear or tensile loads on the fiber-matrix interface. This prevents a gradual detachment of fiber ends from the matrix, which impairs the quality / strength of subsequent adhesive repairs and / or requires a long intermediate fine grinding / polishing process, so that this can generally be omitted when using the invention.

The harmful impairment of the component surface in processes with an active movement tangential to the component surface is also heavily dependent on the state of wear of the tool; however, the present invention eliminates this harmful influence due to the blasting material (abrasive medium) supplied in each case (see Freese, J. de et al .: “End milling of carbon fiber reinforced plastics as surface pretreatment for adhesive bonding - effect of interlaminar damages and particle residues “THE JOURNAL OF ADHESION, https://doi.org/10.1080/00218464.2018.1557054; or Hintze, W .; Hartmann, D .; Schubert, U. "Face milling of CFRP for the production of joining surfaces and preparation for repairs". Z. economic factory operation., Jun, 2012, 107, 462-466. DOI: 10.3139 / 104.110775) .

In contrast to abrasive water jet removal, the present invention avoids an undesired entry of moisture into the damaged component zone. In addition, in contrast to abrasive water jet removal, the invention allows for a largely emission-free removal, i.e. the environment is not contaminated by abrasive particles and removal products.

Up to now, conventional methods such as the known use of vacuum suction jets have only been able to remove the top layer of fiber composites in thin layers at removal rates of 0.2 mm ³ / s. In contrast to this, it has been found that the present invention enables an automatic and controlled process with which uniform and large-area fiber composite layers can be removed at removal depths in both thin and cm areas with removal rates of 5 mm ³ / s and more . Larger areas can thus be removed more quickly, uniformly and homogeneously with an accuracy down to the µm range and, in particular, resin and fiber can also be removed over a large area. A decisive advantage over previous ablation processes and thin-layer grinding is therefore, in addition to the lateral beam area adaptation, in particular the faster and greater ablation rate and a defined scarf course with a higher and defined depth of the ablation. Different composite materials and geometries can be processed with the process. The possible and preferred automation improves ergonomics, safety and process time compared to manual grinding. Another important advantage of the invention is that the abrasive blasting agent is immediately sucked up again together with the resulting FRP grinding dust, so that no dust is released as is the case with classic processes. The suction jet unit therefore works with low emissions, no coolants or subsequent cleaning steps are required. Another great advantage of the invention when removing fiber composite layers is the avoidance of delamination, since the mechanism of action of the material separation is normal to the surface and not tangential. Only negligible mechanical stresses are applied to the component and there is no thermal load (as is the case with the laser process, for example). By means of a depth and width control supported by a 2D sensor and its regulation of removed fiber layers, the quality in particular can be controlled and assured during the process, so that reworking time is saved. Vacuum suction blasting also applies very little forces to the material to be treated when processing lightweight surfaces, which eliminates the problem of force and deformation during repair work. The process is also suitable for various fibers and resin systems and, in contrast to laser ablation, also on conductive materials.

In particular, the invention offers system and method solutions for the repair area and thus for an in-field solution. The area of application is particularly, but not exclusively, the assembly of fiber composite components in the aviation industry (primarily manufacturers and suppliers) in the repair sector, primarily maintenance companies such as the maintenance and repair operations of Lufthansa Technik, for example. The present invention is suitable for in-field processing and repair of fiber composite components, including the processing of large fiber composite structures such as are often found in aircraft construction. Furthermore, the experience gained in the aviation sector, for example, can be easily applied to machining processes on rotor blades in wind energy or in automotive engineering. The process can be used directly on site and thus save enormous costs and time. Another possible area of application is the reworking of manufacturing defects on components during production, in which inline (in Rep-Shops and FAL) reworking in assembly enables fast and clean processing.

In an advantageous embodiment of an aspect of the invention, the pressure gradient is in a range from 200 to 500 hPa, preferably in the range from 275 to 350 hPa. It has been found that good results can be achieved with a pressure gradient in this range.

In another advantageous embodiment of an aspect of the invention, the pressure gradient is provided in such a way that there is a negative pressure in relation to a surrounding atmosphere in the working space. In this embodiment, the invention basically corresponds to the approach of vacuum suction, whereby the pressure gradient can be achieved simply by means of a suitable suction unit with respect to the ambient air.

In another advantageous embodiment of an aspect of the invention, the removal unit is designed so that the working space has a supply of transport gas and / or air between the removal unit and the fiber composite workpiece, the supply preferably having a gap between the removal unit and the fiber composite workpiece with a width in a range from 1/4 to 1/20 of the Distance of the jet pipe to the fiber composite workpiece includes, particularly preferably with a width of less than 0.5 mm. It has been found that a corresponding additional supply of air or transport gas on the one hand influences the pressure gradient as such, but better removal of material is achieved through the additional flow.

In another advantageous embodiment of an aspect of the invention, the blasting material has a spattered grain shape. The more or less pronounced irregularity together with sharp edges of the spattered material has a positive effect on the abrasiveness of the blasting material.

In another advantageous embodiment of an aspect of the invention, the blasting material comprises a ceramic material with a Mohs hardness in the range from 6 to 7.5, silicon dioxide and / or broken glass. It has been found that good properties can be achieved with such a blasting material.

In another advantageous embodiment of an aspect of the invention, the blasting material has an average grain size of 200 to 325 μm. The range given here for the mean grain size is particularly preferred.

In another advantageous embodiment of an aspect of the invention, the blasting material is accelerated with a mass throughput in the range from 120 to 200 g / min, preferably in the range from 140 to 160 g / min. With such a mass throughput, good removal effects can be achieved together with economical use of the blasting material.

In another advantageous embodiment of an aspect of the invention, the blasting material hits the fiber composite workpiece at an angle of 40 ° or less to a respective surface normal of the fiber composite workpiece, preferably at an angle of 25 ° or less, particularly preferably at an angle of 5 ° or less, the respective surface normal being an average surface normal of an area around an impact point with a diameter which is at least 10 times larger than the mean grain size of the blasting material. Even if an approximately vertical impingement of the blasting material is preferred, it has been found that good results can still be achieved even with deviations from the normal. Due to the roughness of the surface caused by the material removal and possibly also by the fiber composite workpiece itself, the surface normal cannot be viewed in the microscopic range or in an even finer range.

In another advantageous embodiment of an aspect of the invention, the jet pipe has a nozzle with a round or rectangular nozzle outlet, preferably with an inside diameter of less than 50 mm, preferably in the range from 10 to 15 mm.

In another advantageous embodiment of an aspect of the invention, the nozzle of the jet pipe is a Venturi nozzle with a constriction area, the inner diameter of which is from 50 to 75% of the nozzle outlet.

In another advantageous embodiment of an aspect of the invention, the removal unit is moved laterally with respect to the fiber composite workpiece at a speed in the range from 1 to 10 mm / s, preferably in the range from 3 to 5 mm / s. It has been found that good results can be achieved with such a speed of movement of the removal unit and thus of the area in which material is removed.

In another advantageous embodiment of an aspect of the invention, the removal unit is moved laterally with respect to the fiber composite workpiece in such a way that an overlap of adjacent removal tracks with a width in the range of 5 to 10% of a track width is achieved. The removal in the removal tracks is generally somewhat less in the edge area, so that overall good uniformity can be achieved with a corresponding overlap.

In another advantageous embodiment of an aspect of the invention, the distance between the jet pipe and the fiber composite workpiece is adapted in accordance with a local amount of material removed. In view of the importance of the distance between the jet pipe and the surface, it can be advantageous to adapt the position of the jet pipe in relation to the surface (or in relation to the “bottom” of the ablation area), depending on the local depth.

In another advantageous embodiment of an aspect of the invention, the material removal according to the invention is carried out as a shaft material removal in a method for repairing a fiber composite workpiece with fibers and resin, which also includes a subsequent lamination or gluing of a repair piece to the fiber composite workpiece in the area of the material removal.

In another advantageous embodiment of an aspect of the invention, the device according to the invention comprises at least one sensor unit for detecting a removal result and a control unit that is used to control the device Is designed based on a detection result of the sensor unit.

Features of advantageous embodiments of the invention are defined in particular in the subclaims, with further advantageous features, designs and configurations for the person skilled in the art also being evident from the above explanation and the following discussion.

• 1 schematische Darstellungen der Einwirkungen bei einem Strahlverfahren und einem Zerspanungsverfahren an einem Verbundwerkstoff,
• 2 eine schematische Darstellung einer mobilen, manuell geführten Strahleinheit,
• 3 eine schematische Darstellung einer Vakuumsaugstrahleinheit mit einer Anbindung an einen Roboter,
• 4 eine schematische Darstellung zur Illustration eines Ausführungsbeispiels der Erfindung,
• 5 eine schematische Darstellung zur weiteren Illustration des Ausführungsbeispiels,
• 6 Beispiele für typische Schäftungsvarianten,
• 7 schematische Darstellungen zur Erläuterung eines Bahnverlaufs bei einer Stufenschäftung,
• 8 schematische Darstellungen von Sollschäftungsgeometrien und jeweiligen Schäden,
• 9 eine schematische Draufsicht eines erfindungsgemäßen Abtragsystems mit einer kontinuierlichen Messung,
• 10 ein Ablaufdiagramm einer Ausgestaltung des erfindungsgemäßen Verfahrens.

In the following, the present invention is further illustrated and explained on the basis of the exemplary embodiments shown in the figures. Here shows

• 1 schematic representations of the effects of a blasting process and a machining process on a composite material,
• 2 a schematic representation of a mobile, manually guided jet unit,
• 3 a schematic representation of a vacuum suction jet unit with a connection to a robot,
• 4th a schematic representation to illustrate an embodiment of the invention,
• 5 a schematic representation to further illustrate the embodiment,
• 6th Examples of typical stock options,
• 7th schematic representations to explain the course of a path in a stepped shoulder,
• 8th schematic representations of nominal shaft geometries and respective damage,
• 9 a schematic top view of a removal system according to the invention with a continuous measurement,
• 10 a flow chart of an embodiment of the method according to the invention.

In the accompanying drawings and the explanations of these drawings, elements that correspond or are related to one another are identified - as far as appropriate - with corresponding or similar reference numerals, even if they are to be found in different exemplary embodiments.

1 shows schematic representations of the effects of a blasting process and a machining process on a composite material 1 . In a blasting method, for example the method according to the invention, the primarily normal effective movement of the blasting agent results 2 (represented by the arrow 4th ) a corresponding normal stress and a perpendicular to the workpiece 1 directed removal. In contrast to this occurs when machining with one cutting edge 3 a primarily tangential active movement (represented by the arrow 5 ) and a shear stress, causing damage here 6th comes.

2 shows a schematic representation of a mobile, manually guided jet unit, as it is basically already known from the prior art. The jet unit comprises a jet nozzle unit 11 or 12th on the one hand with a material feed 13th and on the other hand with an industrial vacuum cleaner 14th is coupled. By the industrial vacuum cleaner 14th The negative pressure caused is from the material feed 13th Blasting material extracted and to the blasting nozzle unit 12th conveyed where the blasting material hits the surface to be processed and then by the vacuum of the industrial vacuum cleaner 14th is discharged together with removed material.

3 shows a schematic representation of a vacuum suction jet unit with a connection to a robot. Similar to the jet unit 2 is blasting material from a deployment 15th from blasting material to one from a robot 16 held jet head 17th led to there on the workpiece 16 to be directed.

While sandblasting accelerates material to the surface with a pressure of typically 6 bar, vacuum suction blasting usually does this with approx. 0.2 bar.

After hitting the workpiece 18th the blasting material is caused by the negative pressure of the vacuum suction device 19th together with from the workpiece 18th dissolved or removed material conveyed away.

4th shows a schematic representation to illustrate an embodiment of the invention, wherein a vacuum suction jet unit is shown.

The vacuum suction jet unit comprises a blasting agent container 21 , which serves as a material supply for providing blasting material, a supply hose 22nd , a jet pipe 23 , a suction tube 24 , a suction hose 25th and a sucker 26th , which serves as a pressure unit to provide a pressure gradient. The jet pipe 23 and the suction tube 24 form in their overall unit a removal unit for removing material from a surface to be processed 27 or from a workpiece. The respective distances of the nozzle 23 and the suction tube 24 to the surface 27 are neither to each other nor to the dimensions of the pipe 23 , 24 true to scale.

5 shows a schematic representation to further illustrate the embodiment. Here are only the jet pipe 23 , the suction tube 24 and the workpiece surface 27 illustrated. Through the nozzle 23 through it becomes blasting material 28 on the surface 27 guided, which is shown by the arrow pointing downwards in the drawing. The blasting material 27 meets the surface 27 and removes material there. As a result of the prevailing pressure gradient, it becomes blasting material 27 and material removed from the workpiece through the area between the suction tube 24 and the nozzle 23 discharged through.

If, as indicated here schematically, between the end of the suction tube 24 and there is a small gap on the surface, air can enter here, the corresponding air flow supporting the removal of the blasting material and the removed material.

6th shows examples of typical stock variants. The left part of 7th shows a step removal in which in the area of the workpiece 31 There are steps, while in the case of an ablation with transition, which is illustrated in the right-hand part, such steps are not present. Between a patch 33 and the workpiece 31 will typically be an adhesive 32 intended.

7th shows schematic representations to explain the course of a path in a stepped shoulder.

With the automated removal process of the stepped stocking, as it is in 7th is illustrated, the first layer of the entire shaft surface is removed first (see left part of 7th ), then the area one step width smaller (see middle and right part of 7th ). The geometry of the treatment area depends on the geometry of the damage. Round or oval shaft profiles can be produced more easily and precisely in the edge area of the steps than rectangular profiles. The upper part of 7th indicates the direction of movement and the shape of the shaft course in plan view, the lower part shows a schematic cross-sectional view.

In the context of the invention, an abrasive stream of preferably silicon oxide blasting media can be used in order to blast onto the fiber composite surfaces and achieve a layer-to-layer removal of fiber composite structures and laminates.

8th shows schematic representations of nominal shaft geometries and respective damage. With a more punctiform damage 41 the corresponding shaft geometry has an essentially round shape, as shown in the left-hand part of 8th is shown. In the case of elongated damage 42 as he did in the right part of 8th is shown, a more oval shaft geometry is preferably provided.

9 shows a schematic top view of an ablation system according to the invention with a continuous measurement.

In the context of the present invention, a process control for controlled removal is provided. The global location and the type of damage geometry are assumed to be known before the start of the process, whereby the methods of damage detection already correspond to the state of the art.

With the help of a robot end effector, the jet head (with jet pipe 23 and outer tube 24 ) positioned. The local starting point of the shaft is determined with the help of an upstream sensor system (eg a 2D line scanner) in order to then follow the programmed path. The direction of movement of the blasting head over the surface (initially the surface to be processed 53 ) is indicated by the arrow 55 indicated.

An optical 2D line sensor system downstream of the blasting head is used for continuous control of the beam removal 51 used with a resolution of 2 µm. This recognizes layer depths of 0.1 mm to 0.2 mm in a measuring width of 25 mm. The beam depth and width achieved are checked and, if necessary, corrected in order to be able to react to changes in beam removal in the 2 ms range during the process. The robot movements and beam parameters are adjusted via a real-time capable program in the controller. The process is corrected using an algorithm if a layer still has to be removed. The normal distance to the surface is measured directly behind the outer jet nozzle. If the blasting process is interrupted, the blasting head and the ablated surface can also be moved 54 subsequently measured. A continuous tracking measurement is the most time-saving option, as measurements can be taken directly while the vehicle is in motion and no additional control drive is necessary. Since the measuring point of the sensor is outside the beam head, the distance is 56 from the measuring point to the point of action through a thin-walled outer tube 24 (approx. 1 mm) kept small in order to enable a quick correction of the removal (e.g. if the depth is not reached, whereby the movement and speed of the blasting head is automatically adjusted in the program). A leading sensor is used as a reference 52 intended.

In contrast to the known approach of the vacuum suction jet process, which is only used for the superficial pretreatment of If fiber composite workpieces are provided in which only the matrix of the cover layer but not the fibers are to be removed, the method according to the invention aims to also remove the fibers and these over a greater depth of the component.

An exemplary embodiment of the invention is explained below.

A mixture of air and abrasive particles is sucked in via a feed channel via a suction channel that is sealed off or largely sealed off from the component surface. In contrast to the suction channel, the supply channel is at a distance from the component surface (see 5 ). The abrasive particles cause material removal through individual impacts on the surface through part of their kinetic energy. The particles are reflected from the component surface as a result of the residual energy and reach the suction channel supported by the negative pressure (vacuum).

The corresponding device includes (cf. also 2 and 3 ) a blasting agent container, a supply hose, a jet pipe, a suction pipe, a suction hose and a vacuum suction device.

In the present embodiment, particles are preferably used with a spattered grain shape, ie with sharp-edged partial surfaces, preferably a ceramic of high hardness, more preferably made of SiO2, preferably as broken glass, the density of which is less than 3.2 g / cm ³ , preferably less than 2.7 g / cm ³ , especially about 2.5 g / cm ³ , and the mean grain diameter of which is at least 200 µm, preferably at least 250 µm, the negative pressure generated in the jet hood at the point of action being between 200 hPa and 500 hPa, preferably between 280 hPa to 330 hPa, wherein the distance between the feed channel (jet pipe) and the point of action on the component surface is 4 to 11 mm, preferably 6 to 9 mm, especially 7 to 8 mm.

The active principle according to the invention is based on an energy-bound removal by a gas-guided particle beam with a predominantly normal direction of action, which has an angle of a maximum of 40 ° to the surface normal, preferably of a maximum of 25 ° to the surface normal, especially with an approximately normal direction of action to the workpiece surface (see 1 ). The removal mechanism is based on the fact that the individual blasting grains, through their kinetic energy, load the material to be separated superficially in a locally extremely limited area, primarily under pressure. In the case of brittle materials such as carbon and glass fibers, the stress concentration leads to brittle fracture. In the case of ductile materials, such as resin matrix and copper mesh for lightning protection, repeated impacts of the abrasive grains lead to local fatigue of the treated material area and ultimately to the superficial detachment of individual particles. Deeper layers of fiber or laminate are therefore not damaged (see 1 ).

The invention implements the vacuum suction blasting process for targeted, large-area removal in width and depth on fiber composite components. The removal includes fibers and matrix. The process using vacuum suction blasting is a novel approach for the precise removal of damaged areas on fiber composite components by means of scarfing. The automation of this process is therefore suitable as a technology solution for the repair of fiber composite components in industry. The process covers different repair point sizes and depths. An ablation geometry adapted to the damaged area can be generated, whereby in particular basic scarfing courses on the scale of a typical scarfing point of approx. 300 mm x 300 mm are produced. This size covers about 90% of the damage in industry.

For this purpose, nominal shaft geometries are created and executed using CAM routines for pocket milling (see 6th ). For repairs in the aviation sector, material-dependent information on the layer thickness is usually used in order to adapt the process and the process parameters to the respective material. Typical material thicknesses of fiber composite components (eg fuselage shells) in aviation are approx. 1 mm to 25 mm with individual layers of approx. 0.15 mm. A gradual removal of approx. 20 mm width per layer is preferred.

For example, a procedure for ablation includes a program selection for the respective ablation process, positioning the blasting head of the robot on the surface, switching on the industrial vacuum cleaner via a program command of the robot program, starting the blasting media supply via a signal in the program, moving the blasting head on the workpiece surface and a control of the removal depth and width by a sensor system and a corresponding control of the program parameters, the program running through to the end of the blasting process.

One embodiment of the method according to the invention is dry processing by means of an abrasive blasting medium in the transport gas conveyed by means of negative pressure in the blasting tube, closed to the processing surface by an outer tube which contains a controlled small gap for a supply air that accelerates the blasting medium flow. The process is distinguished by the fact that for the volumetric removal of fiber resin laminates the arrangement of the jet pipe, the pressure area, the Mass flow and the grain sizes can be set appropriately as main parameters. The negative pressure to be set is between 200 hPa and 500 hPa, preferably 300 hPa. The mass throughput desired for removal can be set in particular between 120 g / min and 200 g / min, preferably 150 g / min. Grain sizes between 200 µm and 500 µm are provided, a broken glass blasting agent with a grain size of 315 µm is preferred.

It has been found that the corresponding device has setting options with regard to jet pipe geometries in particular. In particular, the jet nozzle geometries made of round nozzles, preferably Venturi nozzles (Venturi diameter min. 8 mm, outlet 13.5 mm to max. 20 mm) can be used for the removal. Inner tube diameters can be up to 50 mm, depending on the hose diameter, preferably 10 mm to 15 mm, in order, for example, to enable an optimal and efficient processing width of 20 mm. Nozzles with a round or rectangular outlet can be used. A jet pipe distance of 3 mm to 10 mm to the surface is possible, preferably 7-8 mm should be set. The travel speed with the aforementioned preferred values should be between 1 mm / s and 9 mm / s, preferably 4 mm / s. A web overlap width of 1 mm to 2 mm must be set for a seamless transition between two removal tracks. A flexible sealing material that can be adapted to different component geometries is used to close the jet head to the component, thus creating the necessary negative pressure to separate the repair site from the surroundings.

In a more concrete embodiment, the requirement for a CFRP plate with 300 mm x 300 mm, a layer thickness of 0.125 mm and a top layer 0.06 mm is assumed, with a processing width with steps of 20 mm and removal of three layers.

With the automated removal process of the stepped shaft, first the first layer of the entire shaft surface is removed, then the area one step width smaller. In the case of CFRP components with a top layer, this is first removed; a separate speed is selected for this because the layer is thinner.

An initial state includes, for example, a Kuka robot with suction jet end effector and blasting agent container on a tender wagon, a hose guide connected to an industrial vacuum cleaner, hoses 45 mm, suction hose 30 m, 13 mm blasting hose 10 m, with nozzle geometries made up of round Venturi nozzles (Venturi diameter min. 8 mm , Exit 13.5 mm to max. 20 mm) are provided.

The process here includes that the plate is firmly clamped on a flat table. Two levers on the industrial vacuum cleaner are set to the maximum negative pressure (approx. 300 hPa). The blasting media container is filled with blasting material GB 315 and the inner tube of the blasting nozzle is set at a distance of 7 mm from the surface. A Kuka program is selected for the respective removal process and the blasting head is positioned on the surface by the robot, this comprising a drive to the first position with a distance of the outer nozzle of 1 mm to the surface, with a flexible seal in contact with the surface .

The robot program switches on the industrial vacuum cleaner via a program command, so that the extraction system starts. The delivery rate is around 60% (150 g / min). Then the blasting media supply is started via a signal in the program, i.e. the conveyance is started. A robot movement of 8 mm / s is provided to remove the cover layer in the desired area, with a robot movement of 4 mm / s being set for the remaining layers. When traveling, the distance between the track centers is 13 mm (track overlap width of 1 mm to 2 mm). The blasting head is moved on the workpiece surface with programmed paths. The sensors control the depth and width of the ablation and regulate the program parameters until the blasting process is complete.

10 shows a flow chart of an embodiment of the method according to the invention.

The method is used to remove material from a fiber composite workpiece with fibers and resin.

In step 61 a pressure gradient is provided in a transport gas. In step 62 a blasting material is provided. The steps 61 and 62 are shown here in parallel, but can also be provided consecutively or only partially overlapping.

As a result of the pressure gradient in step 63 blasting material is accelerated onto a surface of the fiber composite workpiece so that it is in step 64 comes to an abrasive removal of material including fibers and resin from the fiber composite workpiece in a working space determined by a removal unit and the fiber composite workpiece. In step 65 removed material and blasting material is carried away from the working area by the pressure gradient.

According to the invention, the blasting material is passed through a blasting tube onto the surface of the fiber composite workpiece, the blasting material having an average grain size in the range from 200 µm to 500 µm and the distance between the beam tube and the fiber composite workpiece in the working area being in a range of 3 to 12 mm.

Even if various aspects or features of the invention are each shown in combination in the figures, it is clear to the person skilled in the art - unless stated otherwise - that the combinations shown and discussed are not the only possible ones. In particular, corresponding units or feature complexes from different exemplary embodiments can be exchanged with one another.

List of reference symbols

1

Composite

2

Abrasives

3

Cutting edge

4th

Active movement of the abrasive

5

Effective movement of the cutting edge

6th

Injuries

11, 12

Jet nozzle unit

13th

Material feed

14th

Industrial vacuum cleaner

15th

Provision of blasting material

16

robot

17th

Jet head

18th

workpiece

19th

Vacuum cups

21

Abrasive container

22nd

Feed hose

23

Jet pipe

24

Suction tube

25th

Suction hose

26th

Mammal

27

surface

28

Blasting material

31

workpiece

32

adhesive

33

Patch

41

punctiform damage

42

elongated damage

51

lagging sensor

52

leading sensor

53

surface to be removed

54

worn surface

55

Direction of movement

56

distance

61

Providing a pressure gradient

62

Provision of blasting material

63

Accelerating blasting material

64

Abrasive removal

65

Discharge of material

QUOTES INCLUDED IN THE DESCRIPTION

This list of the documents listed by the applicant was generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Patent literature cited

• EP 2442941 B1 [0012, 0016]
• DE 102010020691 A1 [0016]
• DE 19747838 C2 [0016]
• DE 102010060664 A1 [0016]
• EP 1136174 A1 [0016]
• US 2004053561 A1 [0016]

Non-patent literature cited

• N. Bhatnagar, N. Ramakrishnan, N.K. Naik, R. Komanduri "On the machining of fiber reinforced plastic (FRP) composite laminates." International Journal of Machine Tools & Manufacture 1995 [0004]
• Freese, J. de et al .: "End milling of Carbon Fiber Reinforced Plastics as surface pretreatment for adhesive bonding - effect of interlaminar damages and particle residues" THE JOURNAL OF ADHESION, https://doi.org/10.1080/00218464.2018.1557054 ; or Hintze, W .; Hartmann, D .; Schubert, U. "Face milling of CFRP for the production of joining surfaces and preparation for repairs". Z. economic factory operation., Jun, 2012, 107, 462-466. DOI: 10.3139 / 104.110775) [0034]

Claims (17)

Method for material removal from a fiber composite workpiece with fibers and resin, with the steps: Providing a pressure gradient in a transport gas, Providing a blasting material, Accelerating the blasting material through the pressure gradient on a surface of the fiber composite workpiece, abrasive removal of material including fibers and resin from the fiber composite workpiece in a working space determined by a removal unit and the fiber composite workpiece and Removal of removed material and blasting material from the work area through the pressure gradient, whereby the blasting material is directed through a blasting tube onto the surface of the fiber composite workpiece, characterized in that the blasting material has an average grain size in the range from 200 µm to 500 µm and a distance between the jet pipe and the fiber composite workpiece in the work area is in a range of 3 to 12 mm. Procedure according to Claim 1 , the pressure gradient being in a range from 200 to 500 hPa, preferably in the range from 275 to 350 hPa. Method according to one of the preceding claims, wherein the pressure gradient is provided in such a way that there is a negative pressure in relation to a surrounding atmosphere in the working space. The method according to any one of the preceding claims, wherein the removal unit is designed such that the working space has a supply of transport gas and / or air between the removal unit and the fiber composite workpiece, wherein the supply preferably has a gap between the removal unit and the fiber composite workpiece with a width of one Range from 1/4 to 1/20 of the distance between the jet pipe and the fiber composite workpiece, particularly preferably with a width of less than 0.5 mm. Method according to one of the preceding claims, wherein the blasting material has a spattered grain shape. Method according to one of the preceding claims, wherein the blasting material comprises a ceramic material with a Mohs hardness in the range from 6 to 7.5, silicon dioxide and / or broken glass. Method according to one of the preceding claims, wherein the blasting material has an average grain size of 200 to 325 µm. Method according to one of the preceding claims, wherein the acceleration of the blasting material takes place with a mass throughput in the range from 120 to 200 g / min, preferably in the range from 140 to 160 g / min. Method according to one of the preceding claims, wherein the blasting material hits the fiber composite workpiece at an angle of 40 ° or less to a respective surface normal of the fiber composite workpiece, preferably at an angle of 25 ° or less, particularly preferably at an angle of 5 ° or less less, the respective surface normal being an average surface normal of a region around an impact point with a diameter which is at least 10 times larger than the mean grain size of the blasting material. Method according to one of the preceding claims, wherein the jet pipe has a nozzle with a round or rectangular nozzle outlet, preferably with an inside diameter of less than 50 mm, preferably in the range from 10 to 15 mm. A method according to any one of the preceding claims, wherein the nozzle of the jet pipe is a venturi nozzle with a constriction area, the inner diameter of which is from 50 to 75% of the nozzle outlet. Method according to one of the preceding claims, wherein the removal unit is moved laterally with respect to the fiber composite workpiece at a speed in the range from 1 to 10 mm / s, preferably in the range from 3 to 5 mm / s. Method according to one of the preceding claims, wherein the removal unit is moved laterally with respect to the fiber composite workpiece in such a way that an overlap of adjacent removal tracks with a width in the range of 5 to 10% of a track width is achieved. Method according to one of the preceding claims, wherein the distance between the jet pipe and the fiber composite workpiece is adapted in accordance with a local amount of material removed. Method for repairing a fiber composite workpiece with fibers and resin, with the steps: Sharp material removal with the steps of the method according to one of the preceding claims, Laminating or gluing a repair piece to the fiber composite workpiece in the area of material removal. Device for automated material removal from a fiber composite workpiece with fibers and resin, comprising: a pressure unit, which is designed to provide a pressure gradient in a transport gas, a material supply, which is designed to provide a blasting material, and a removal unit with a jet pipe, the device for this purpose is designed to accelerate and guide the blasting material provided by the material supply onto a surface of the fiber composite workpiece through a pressure gradient provided by the pressure unit, so that an abrasive removal of material including fibers and resin from the fiber composite workpiece in one by a removal unit and the fiber composite workpiece specific working space is effected, wherein the device is further designed for removing removed material and blasting material from the working space by the pressure gradient, characterized in that the blasting material is a medium Has grain size in the range from 200 µm to 500 µm and, when the device is in operation, the distance between the jet pipe and the fiber composite workpiece in the working space is in a range from 3 to 12 mm. Device according to Claim 16 , further with at least one sensor unit for detecting a removal result and a control unit which is designed to control the device on the basis of a detection result of the sensor unit.

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